Lithography Process and Material for Negative Tone Development

ABSTRACT

The present disclosure provides resist rinse solutions and corresponding lithography techniques that achieve high pattern structural integrity for advanced technology nodes. An example lithography method includes forming a resist layer over a workpiece, exposing the resist layer to radiation, developing the exposed resist layer using a developer that removes an unexposed portion of the exposed resist layer, thereby forming a patterned resist layer, and rinsing the patterned resist layer using a rinse solution. The developer is an organic solution, and the rinse solution includes water.

PRIORITY DATA

This application claims priority to U.S. patent application Ser. No.16/102,908 filed on Aug. 14, 2018, entitled “Lithography Process andMaterial for Negative Tone Development,” the entire disclosure of whichis hereby incorporated by reference.

BACKGROUND

Lithography is extensively utilized in integrated circuit (IC)manufacturing, where various IC patterns are transferred to a workpieceto form an IC device. A lithography process typically involves forming aresist layer over the workpiece, exposing the resist layer to patternedradiation, and developing the exposed resist layer, thereby forming apatterned resist layer. As IC technologies continually progress towardssmaller technology nodes, the structural integrity of resist patternsbecomes more vulnerable, as resist patterns are more prone todeformation, collapse, and/or peeling. Multiple factors affect theseparameters, among which are the choice of developers and rinse solutionsused on an exposed resist layer. Positive tone development (PTD) whichremoves exposed portions of the resist layer and negative tonedevelopment (NTD) which removes unexposed portions of the resist layeroften use different developers and rinse solutions. Current PTD and NTDprocesses lead to various resist structural issues. Accordingly,although existing lithography techniques have been generally adequatefor their intended purposes, they have not been entirely satisfactory inall respects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a flow chart of a lithography method for processing aworkpiece according to various aspects of the present disclosure.

FIGS. 2A, 2B, 2C, 2D, 2E, and 2F are fragmentary cross-sectional viewsof a workpiece at various fabrication stages according to variousaspects of the present disclosure.

FIG. 3 is a simplified schematic diagram showing certain molecules in anexposed portion of a patterned resist layer according to various aspectsof the present disclosure.

FIG. 4 is a simplified block diagram of a developing and rinsing systemaccording to various aspects of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to methods for manufacturingintegrated circuit (IC) devices, and more particularly, to lithographytechniques and/or lithography materials implemented during manufacturingof IC devices.

The following disclosure provides many different embodiments, orexamples, for implementing different features. Reference numerals and/orletters may be repeated in the various examples described herein. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various disclosed embodimentsand/or configurations. Further, specific examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact. Moreover, the formation of afeature on, connected to, and/or coupled to another feature in thepresent disclosure may include embodiments in which the features areformed in direct contact, and may also include embodiments in whichadditional features may be formed interposing the features, such thatthe features may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” etc., may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in figures. The spatially relative terms areintended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Forexample, if the device in the figures is turned over, elements describedas being “below” or “beneath” other elements or features would then beoriented “above” the other elements or features. Thus, the example term“below” can encompass both an orientation of above and below. Anapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors may likewise beinterpreted accordingly.

Lithography generally uses one of two types of developing processes: apositive tone development (PTD) process and a negative tone development(NTD) process. The PTD process uses a positive tone developer, whichgenerally refers to a developer that selectively dissolves and removesexposed portions of the resist layer. The NTD process uses a negativetone developer, which generally refers to a developer that selectivelydissolves and removes unexposed portions of the resist layer. The PTDprocess uses water-based developers and water-based rinse solutions. TheNTD process uses organic-based developers and organic-based rinsesolutions. Both PTD processes and NTD processes have drawbacks whenattempting to meet lithography resolution demands for advancedtechnology nodes. For example, both PTD processes and NTD processes(particularly those using NTD developers that include n-butyl acetatesolvents) have been observed to cause resist pattern swelling, leadingto insufficient contrast between exposed portions and unexposed portionsof the resist layer (in other words, poor resist contrast) and resultingin deformation, collapse, and/or peeling problems. In NTD, organic-baseddevelopers and organic-based rinse solutions are both prone to softenthe resist (by causing the resist to swell), thereby damaging structuralintegrity of resist patterns. However, NTD typically provides betternormalized image log-slope (NILS) than PTD. For this reason, NTD hasbecome the focus for improving resolution for advanced technology nodes.

The present disclosure thus explores NTD-related materials andtechniques that can improve the structural integrity of resist patterns.For example, the present disclosure solves issues in existing NTDapproaches by changing the composition of rinse solutions. In someembodiments, instead of using purely organic solvents in a rinsesolution, water is added to the rinse solution to significantly increaseits chemical polarity, which in turn reduces its softening of resistpatterns. Hydrogen bonds may be formed between water molecules andpolymer molecules to “harden” the resist patterns. In some embodiments,the rinse solution includes other components such as a dipole solventwhich helps the rinse solution to mix with the organic-based developer,a low surface tension solvent which helps the rinse solution to providegood “coverage” over the entire surface of patterned resist layer, and acrosslinking agent which helps linking together polymer chains withinthe resist pattern. The composition of the rinse solution is carefullyconfigured herein to achieve effective rinsing while enhancing thestructural integrity of patterned resist layer.

FIG. 1 is a flow chart of a lithography method 100 for processing aworkpiece (e.g., a substrate) according to various aspects of thepresent disclosure. In some implementations, method 100 is implemented,in whole or in part, by a system employing advanced lithographyprocesses, such as deep ultraviolet (DUV) lithography, extremeultraviolet (EUV) lithography, e-beam lithography, x-ray lithography,and/or other lithography to enhance lithography resolution.

The steps of FIG. 1 are first introduced briefly and then elaborated inconnection with FIGS. 2A-2F. At block 102, a resist layer is formed overa material layer of a workpiece. In some implementations, the resistlayer is a negative tone resist, and the material layer is a portion ofa wafer (or substrate). At block 104, the resist layer is exposed toradiation in the form of electromagnetic waves. In some implementations,the resist layer is exposed to patterned EUV radiation. At block 106,the exposed resist layer is baked at an elevated temperature using apost-exposure baking (PEB) process. At block 108, the baked resist layeris developed using a developer, which is an organic solvent. Thedeveloper dissolves or otherwise removes unexposed portions of theresist layer. At block 110, the developed resist layer is rinsed using arinse solution.

Note that additional steps can be provided before, during, and aftermethod 100, and some of the steps described can be moved, replaced, oreliminated for additional embodiments of method 100. For example, atblock 112, method 100 can proceed with additional fabrication steps onthe workpiece. In an embodiment, block 112 includes a fabricationprocess using the patterned resist layer as a mask to pattern thematerial layer on the workpiece. Specifically, the material layer isetched, such that the material layer includes a pattern correspondingwith a pattern of the patterned resist layer. In some implementations,doped regions are formed in the material layer, such that the materiallayer includes doped regions a pattern corresponding with a pattern ofthe patterned resist layer.

FIGS. 2A-2F are fragmentary cross-sectional views of a workpiece 200, inportion or entirety, at various fabrication stages (such as thoseassociated with method 100) according to various aspects of the presentdisclosure. Workpiece 200 is depicted at an intermediate stage offabrication (or processing) of an IC device, such as a microprocessor, amemory, and/or other IC device. In some implementations, workpiece 200may be a portion of an IC chip, a system on chip (SoC), or portionthereof, that includes various passive and active microelectronicdevices, such as resistors, capacitors, inductors, diodes, p-type fieldeffect transistors (PFETs), n-type field effect transistors (NFETs),metal-oxide semiconductor field effect transistors (MOSFETs),complementary metal-oxide semiconductor (CMOS) transistors, bipolarjunction transistors (BJTs), laterally diffused MOS (LDMOS) transistors,high voltage transistors, high frequency transistors, fin-like fieldeffect transistors (FinFETs), other suitable IC components, orcombinations thereof. FIGS. 2A-2F have been simplified for the sake ofclarity. Additional features can be added in workpiece 200, and some ofthe features described below can be replaced, modified, or eliminated inother embodiments of workpiece 200.

In FIG. 2A, workpiece 200 includes a substrate 202. Substrate 202 mayinclude a semiconductor substrate (e.g., a wafer), a mask (also called aphotomask or reticle), or any base material on which processing may beconducted to provide layers of material to form various features of anIC device. Depending on an IC fabrication stage, substrate 202 includesvarious material layers (e.g., dielectric layers, semiconductor layers,and/or conductive layers) configured to form IC features (e.g., dopedregions/features, isolation features, gate features, source/drainfeatures (including epitaxial source/drain features), interconnectfeatures, other features, or combinations thereof). In the depictedembodiment, substrate 202 includes a semiconductor substrate, such as asilicon substrate. Substrate 202 may include another elementarysemiconductor, such as germanium; a compound semiconductor, such assilicon carbide, gallium arsenide, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductor, suchas SiGe, GaAsP, AlInAs, AlGaAs, GalnAs, GaInP, and/or GaInAsP; orcombinations thereof. Alternatively, substrate 202 is asemiconductor-on-insulator substrate, such as a silicon-on-insulator(SOI) substrate, a silicon germanium-on-insulator (SGOI) substrate, or agermanium-on-insulator (GOI) substrate. Semiconductor-on-insulatorsubstrates can be fabricated using separation by implantation of oxygen(SIMOX), wafer bonding, and/or other suitable methods. In someimplementations, where workpiece 200 is fabricated into a mask forpatterning IC devices, substrate 202 can be a mask substrate thatincludes a transparent material (e.g., calcium fluoride (CaF₂)) or a lowthermal expansion material (e.g., fused quartz, TiO₂ doped SiO₂, orother suitable low thermal expansion materials).

A material layer 204 to be processed (also referred to herein as anunderlying layer) is disposed over substrate 202. However, the presentdisclosure contemplates implementations where material layer 204 isomitted, such that substrate 202 is directly processed. In someimplementations, material layer 204 includes a conductive material or asemiconductor material, such as metal or metal alloy. In someimplementations, the metal includes titanium (Ti), aluminum (Al),tungsten (W), tantalum (Ta), copper (Cu), cobalt (Co), ruthenium (Ru),other suitable metal, or combinations thereof. In some implementations,the metal alloy includes metal nitride, metal sulfide, metal selenide,metal oxide, metal silicide, other suitable metal alloy, or combinationsthereof. For example, in some implementations, material layer 204includes titanium nitride (TiN), tungsten nitride (WN₂), or tantalumnitride (TaN).

Alternatively, material layer 204 includes a dielectric material, suchas silicon oxide (SiO₂), silicon nitride (SiN), metal oxide, or metalnitride. For example, material layer 204 may include SiO₂, SiN, siliconoxynitride (SiON), silicon carbon nitride (SiCN), silicon carbide (SiC),aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), or lanthanum oxide(La₂O₃). In some implementations, material layer 204 is a hard masklayer to be patterned for use in subsequent processing of workpiece 200.In some implementations, material layer 204 is an anti-reflectivecoating (ARC) layer. In some implementations, material layer 204 is alayer to be used for forming a gate feature (e.g., a gate dielectricand/or a gate electrode), a source/drain feature (e.g., an epitaxialsource/drain), and/or a contact feature (e.g., a conductive ordielectric feature of a multilayer interconnect (MLI)) of workpiece 200.In some implementations, where workpiece 200 is fabricated into a maskfor patterning IC devices, material layer 204 is a layer to be processedto form an IC pattern therein, such as an absorber layer (including, forexample, chromium) or a reflective layer (including, for example,multiple layers formed on substrate 202, where the multiple layersinclude a plurality of film pairs, such as molybdenum-silicide (Mo/Si)film pairs, molybdenum-beryllium (Mo/Be) film pairs, or other suitablematerial film pairs configured for reflecting radiation).

In FIG. 2B, a resist layer 206 is formed over substrate 202 by asuitable process (e.g., block 102 of method 100). Resist layer 206 isalso called a photoresist layer, photosensitive layer, imaging layer,patterning layer, or radiation sensitive layer. Resist layer 206 issensitive to radiation used during a lithography exposure process, suchas DUV radiation, EUV radiation, e-beam radiation, ion beam radiation,and/or other suitable radiation. In the depicted embodiment, resistlayer 206 includes a material sensitive to EUV radiation. In someimplementations, resist layer 206 is formed by spin coating a liquidresist material onto a material layer to be processed, such as materiallayer 204. After spin coating the liquid resist material (but beforeperforming an exposure process), a pre-bake process can be performed onresist layer 206, for example, to evaporate solvent and to densify theliquid resist material formed over material layer 204.

In some embodiments, resist layer 206 includes a negative tone material(sometimes called a negative tone resist), where portions of resistlayer 206 exposed to radiation become insoluble (or exhibit reducedsolubility) to a developer, and unexposed portions of resist layer 206remain soluble to the developer. Resist layer 206 may include achemically amplified resist (CAR) material. In some implementations, theCAR material includes a polymer and/or other suitable resist componentsmixed in a solvent, which are configured to provide the negative tonematerial. The other resist components can include a photo acid generator(PAG) component, a thermal acid generator (TAG) component, an acidlabile group (ALG) component, a quencher component, a photo-decomposablebase (PDB) component, a chromophore component, a cross-linker component,a surfactant component, and/or other suitable component depending onrequirements of the CAR material. In some implementations, the CARresist material includes the PAG component, which generates acid uponabsorbing radiation. In the depicted embodiment, where resist layer 206is a negative tone resist layer, acid generated from the PAG componentcatalyzes cross-linking of polymer in the CAR resist material and/orsuppressing reactions of other resist components with polymer in the CARresist material, changing characteristics (e.g., polarity and/orsolubility) of exposed portions of resist layer 206. For example, whenresist layer 206 is exposed with radiation reaching a defined exposuredose threshold, exposed portions of resist layer 206 exhibit decreasedsolubility in (and/or increased hydrophobicity to) a developer.

In FIG. 2C, an exposure process is performed on resist layer 206 (e.g.,block 104 of method 100), where resist layer 206 is illuminated withpatterned radiation 208. In some implementations, patterned radiation208 has a wavelength less than about 250 nm, such as DUV radiation(e.g., 248 nm radiation from a KrF laser or 193 nm radiation from an ArFlaser), EUV radiation, x-ray radiation, e-beam radiation, ion-beamradiation, and/or other suitable radiation. In the depicted embodiment,patterned radiation 208 is EUV radiation, which may refer to radiationhaving a wavelength of about 1 nm to about 100 nm. In someimplementations, the EUV radiation has a wavelength of about 10 nm toabout 15 nm (e.g., about 13.5 nm). The exposure process can be in air,liquid (immersion lithography), or vacuum (e.g., when implementing EUVlithography and/or e-beam lithography). In some implementations, theradiation is patterned using a mask having an IC pattern definedtherein, such that the patterned radiation forms an image of the ICpattern on resist layer 206. The mask transmits, absorbs, and/orreflects the radiation depending on the IC pattern, along with masktechnologies used to fabricate the mask. In some implementations, theradiation beam is patterned by directly modulating the radiation beamaccording to an IC pattern without using a mask (sometimes calledmaskless lithography).

A latent pattern is formed on resist layer 206 by the exposure process.The latent pattern is formed on the resist layer, which eventuallybecomes a physical resist pattern when the resist layer is subjected todeveloping and rinsing processes. The latent pattern includes exposedportions 206 a and unexposed portions 206 b (which may include bothunexposed portions and under-exposed portions of resist layer 206). Asshown in FIG. 2C, exposed portions 206 a physically and/or chemicallychange in response to the exposure process. For example, PAG componentsin exposed portions 206 a of resist layer 206 generate acid uponabsorbing radiation, which functions as a catalyst for causing chemicalreactions that decrease (or increase) solubility of exposed portions 206a. For example, acid generated from the PAG components catalyzescross-linking of polymer and/or suppressing reactions of other resistcomponents (such as ALG components) with polymer in exposed portions 206a of resist layer 206, thereby chemically changing exposed portions 206a.

After the exposure process, a post-exposure baking (PEB) process (e.g.,block 106 of method 100) may be performed on resist layer 206. PEB canpromote the cross-linking of polymer and/or suppression of reactions ofother resist components with the polymer. Depending on the polymer(s)included in resist layer 206, PEB may catalyze a reaction betweenreacted photosensitive moieties and the polymer in resist layer 206. Anysuitable baking conditions (e.g., duration or temperature profiles,baking cycles) may be used. In the depicted embodiment, the exposureprocess and/or the PEB process increase the polarity of exposed portions206 a, decreasing solubility of exposed portions 206 a to a developerwith relatively low polarity. In contrast, the polarity of unexposedportions 206 b remains low (or increases less than exposed portions 206a) after the PEB process, so unexposed portions 206 b are more solublein a developer with relatively low polarity.

In FIG. 2D, a developing process is performed on resist layer 206 (e.g.,block 108 of method 100), thereby forming a patterned resist layer 206′.In the depicted embodiment, an NTD process is performed to removeunexposed portions 206 b of patterned resist layer 206′. For example, anNTD developer 210 is applied to resist layer 206 that dissolvesunexposed portions 206 b, leaving patterned resist layer 206′ havingopening(s) 212 defined therein between exposed portions 206 a(collectively called a resist pattern). Since NTD developer 210 isorganic solvent-based, suitable organic solvents include n-butylacetate, ethanol, hexane, benzene, toluene, and/or other suitablesolvents. In some implementations, NTD developer 210 contains no water(it is understood that de minimis amount of water content may bepresent, for example, due to humidity in surrounding environment orother incidental reasons). Applying NTD developer 210 may includespraying NTD developer 210 on patterned resist layer 206′ by aspin-coating process.

In FIG. 2E, a rinse process is performed after the developing process,for example, to remove any residue and/or particles from workpiece 200(e.g., block 110 of method 100). In the depicted embodiment, a rinsesolution 216 is applied to patterned resist layer 206′ to removeunwanted materials. Existing developers and rinse solutions both useorganic solvents. Although the organic solvents are generally adequatefor their intended purposes, they often lead to various issues,especially when technology nodes become smaller (e.g., 20 nm, 10 nm, 7nm, and beyond). For instance, during the development process, theorganic solvent is prone to penetrate into the photoresist and softenthe photoresist (e.g., by causing the photoresist to swell in volume),thereby damaging structural integrity of photoresist patterns. Theissues become more serious with smaller patterns because the softeningis more likely to induce pattern deformation, collapse, and/or peeling.Existing rinse solutions exacerbate such issues because they are alsoorganic solvents. In chemistry, the “like dissolves like” theoryprovides that polar solutions dissolve polar substances and non-polarsolutions dissolve non-polar substances. Therefore, organic solventsused in developing and rinsing are prone to soften the photoresistbecause the organic solvents and the photoresist share similarpolarities.

The present disclosure solves issues in existing approaches by changingthe composition of rinse solutions. Water, such as de-ionized water(DIW), is added to rinse solution 216 to increase the overall polarityof rinse solution 216, which in turn reduces softening of patternedresist layer 206′. In some embodiments, the polarity of rinse solution216 is higher than the polarity of NTD developer 210, or the polarity ofpatterned resist layer 206′ (including both exposed portions 206 a andunexposed portions 206 b), or both. That is, rinse solution 216 has arelatively high polarity. Accordingly, the polarity of rinse solution216 may be designed according to the polarity of NTD developer 210and/or resist layer 206. In some embodiments, the term “polarity”describes a dipole moment. Therefore, the overall dipole moments ofpolarity molecules of rinse solution 216 may be higher than either oneor both of the overall dipole moment of polarity molecules of NTDdeveloper 210 and resist layer 206. As rinse solution 216 includesvarious components, the overall polarity of rinse solution 216 may becomputed using any suitable manner (e.g., a weighted combination ofcomponents).

The water content in rinse solution 216 also improves structuralstability of patterned resist layer 206′ via hydrogen bonds. FIG. 3 is asimplified schematic diagram of certain molecules in an exposed portion206 a after the rinsing process. Exposed portion 206 a contains polymermolecules 310, which have polar functional groups (represented by P1 andP2) that interact with water molecules (represented by HOH). As shown inFIG. 3, when a water molecule penetrates into exposed portion 206 a, oneor more hydrogen bonds 320 may be formed between the water molecule andpolar functional group P1, or P2, or both. Water molecules and hydrogenbonds 320 link multiple polymer molecules 310 together to form longerpolymer chains, which in a sense “hardens” exposed portion 206 a. Watermolecules may additionally interact with polymer molecules 310 viadipole-dipole interactions. Water does not otherwise dissolve polymermolecules 310. Therefore, water in rinse solution 216 enhancesstructural stability of patterned resist layer 206′ by reducing patterndeformation, collapse, and/or peeling. The polar functional groups P1and P2 may include —OH, —COO, COOH, —NH, —S, —SO, lactone, or othersuitable polar functional groups, or combinations thereof. Note that,although the present disclosure uses water as an example hardeningchemical because of its ability to form strong hydrogen bonds withpolymer molecules, other suitable chemicals may also be used if theyrealize similar effect.

The composition of rinse solution 216 is carefully configured herein toachieve optimal result. For instance, the amount of water added to rinsesolution 216 is designed to be within a specific range because, eventhough water helps reduce or avoid softening of patterned resist layer206′, too much water in rinse solution 216 may negatively impact theability of rinse solution 216 to rinse patterned resist layer 206′. Thereason is that, even though most of NTD developer 210 is spun off of thesurface of patterned resist layer 206′ during the development process, alayer of NTD developer 210 may still remain on the surface of patternedresist layer 206′ after the development process. If rinse solution 216contains too much water, rinse solution 216 may not mix well with NTDdeveloper 210 due to significant difference in polarities. If rinsesolution 216 does not penetrate the layer of NTD developer 210, rinsesolution 216 cannot reach the surface of patterned resist layer 206′ foreffective rinsing. Further, water has high surface tension and may noteffectively reach certain surface areas of patterned resist layer206′(e.g., near bottom corners with odd angles). Therefore, waterconstitutes between about 1% and about 30% of rinse solution 216 (e.g.,about 15% in an example, or between about 5% and about 20% in anotherexample). Unless otherwise noted, percentages herein designatepercentages by weight. Note that, in some embodiments, the amount ofwater is at least about 5% to ensure sufficient increase in the overallpolarity of rinse solution 216. Further, since the rinsing processinvolves spinning workpiece 200, the amount of water may increase (e.g.,from about 5% to a higher percentage) during and after the rinsingprocess, as other solvent(s) that have lower boiling points than waterget spun off from workpiece 200.

Rinse solution 216 may include water and one or more organic solvents.In some embodiments, rinse solution 216 includes a dipolar solvent suchas diol, diacid, and/or diamine. Molecules of the dipolar solvent mayalso interact with polymer molecules 310, for example, throughdipole-dipole interactions or hydrogen bonds. The dipole solvent may notinteract with polymer molecules 310 as strongly as water does, but thedipole solvent has good mixing ability with NTD developer 210.Therefore, a suitable amount of dipolar solvent helps reach optimalrinsing result. In some embodiments, the dipolar solvent constitutesbetween about 5% to about 70% of rinse solution 216, where the lowerlimit ensures mixing ability with NTD developer 210, while the upperlimit is determined by the amount of water in rinse solution 216 (e.g.,if rinse solution 216 has about 30% of water it cannot have more thanabout 70% of dipolar solvent). In an embodiment, diamine is used as thedipolar solvent because it mixes well in both water and theorganic-based NTD developer 210 and because it forms strong hydrogenbonds with exposed portion 206 a.

In some embodiments, rinse solution 216 includes a low surface tensionsolvent that has a surface tension lower than a predetermined threshold(e.g., about 35 dyn/cm against air). Since water has high surfacetension (about 72-73 dyn/cm against air), if rinse solution 216 containsonly water it may not have sufficient wettability to reach certainsurface areas of patterned resist layer 206′ (e.g., near bottom cornerswith odd angles). The low surface tension solvent lowers the overallsurface tension of rinse solution 216, and in turn, helps rinse solution216 provide good “coverage” over the entire surface of patterned resistlayer 206′. In some embodiment, the low surface tension solvent includesdiethylene glycol (with a surface tension of about 30 dyn/cm), ordiamine (some with a surface tension of about 31 dyn/cm), or othersuitable solvents, or combinations thereof. In some embodiment, thedipolar solvent and the low surface tension solvent are the same solvent(e.g., diamine). The low surface tension solvent may or may not formhydrogen bonds.

In some embodiments, the low surface tension solvent constitutes betweenabout 10% to about 70% of rinse solution 216, where the lower limitensures wettability, while the upper limit is determined by the amountof water in rinse solution 216 (e.g., if rinse solution 216 has about30% of water it cannot have more than about 70% of low surface tensionsolvent). In some embodiments, although the low surface tension solventitself may have a surface tension as low as about 25%, its volume islimited such that the overall surface tension of rinse solution 216(after components are mixed) is about 35 dyn/cm or higher. Maintainingthe overall surface tension of rinse solution 216 helps reduce or avoidthe softening problems described above. In some embodiments, the overallsurface tension of rinse solution 216 is higher than the surface tensionof NTD developer 210, which is below about 35 dyn/cm.

In some embodiments, rinse solution 216 includes a crosslinking agent,which is a solute that can crosslink with polymer molecules 310 ofpatterned resist layer 206′. The crosslinking agent is an organicmaterial, such as diamine or carbodiimide, that may form covalent bondswith functional groups of polymer molecules 310. For example, thecrosslinking agent may have two polar functional groups that covalentlybond with two COOH groups of two polymer molecules 310. The crosslinkinghelps harden patterned resist layer 206′. In some embodiments, thecrosslinking agent constitutes between about 0.01% to about 15% of rinsesolution 216, where the lower limit ensures sufficient crosslinking ofpatterned resist layer 206′, while the upper limit is determined by thesolubility of the crosslinking agent within rinse solution 216 (e.g., ifrinse solution 216 has about 30% of water and if water cannot dissolvemore than about 50% of crosslinking agent, the crosslinking agent islimited to about 15%).

As described above, various components (including both solvent andsolute) in rinse solution 216—such as water, dipolar solvent, lowsurface tension solvent, and/or crosslinking agent—are carefullyconfigured herein to achieve optimal results (effective rinsing whilemaintaining the structural integrity of patterned resist layer 206′).Both the types and relative quantities of these components may beselected in a combinatory fashion. In some embodiments, rinse solution216 includes about 20% of water, 10%-20% of dipolar solvent, 60-70% oflow surface tension solvent, while the crosslinking agent makes up therest. In an embodiment, rinse solution 216 includes about 20% of water,about 15% dipolar solvent, about 64% of low surface tension solvent, andabout 1% of crosslinking agent. As further described below, rinsingconditions such as duration, temperature, and spin speed may also betailored to achieve optimal results.

After the rinsing process, in some implementations a post-developmentbaking (PDB) process is performed, for example, to further enhancestructural stability of patterned resist layer 206′. The PDB process maybe performed in a chamber (e.g., a hot plate) with an oven tool insemiconductor fabrication.

Referring now to FIG. 2F, an additional fabrication process is performedon workpiece 200 using patterned resist layer 206′ as a mask (e.g.,corresponding to block 112 of method 100). For example, the fabricationprocess is applied within opening(s) of patterned resist layer 206′,while other portions of workpiece 200 covered by patterned resist layer206′ are protected from being impacted by the fabrication process. Insome implementations, the fabrication process etches material layer 204using patterned resist layer 206′ as an etching mask. A pattern is thustransferred from patterned resist layer 206′ to material layer 204,thereby forming patterned material layer 204′ with patterns 204 a. Theetching process may include a dry etching process, a wet etchingprocess, other suitable etching process, or combinations thereof.Alternatively, the fabrication process may include an implantationprocess on material layer 204 using patterned resist layer 206′ as animplant mask, thereby forming various doped features (regions) inmaterial layer 204. Thereafter, as depicted in FIG. 2E, patterned resistlayer 206′ is removed from workpiece 200, leaving patterned materiallayer 204′ disposed over substrate 202. The present disclosure alsocontemplates implementations where, instead of patterning material layer204, a deposition process is performed to fill opening(s) 212 ofpatterned resist layer 206′ with a material, thereby forming IC features(e.g., conductive material lines) over material layer 204.

In some implementations, NTD developer 210 and rinse solution 216 areapplied to workpiece 200 in a developing and rinsing system. FIG. 4 is asimplified block diagram of a developing and rinsing system 300, whichcan be implemented for developing and rinsing resist layer 206 accordingto various aspects of the present disclosure. Developing and rinsingsystem 300 includes a wafer stage 352 having a workpiece (e.g.,workpiece 200) secured thereon by a vacuum mechanism, e-chucking, orother suitable mechanism. A motion mechanism 354 integrated with waferstage 352 drives wafer stage 352, such that wafer stage 352 spinsworkpiece 200 during a developing process. In some implementations,motion mechanism 354 includes a motor to drive wafer stage 352 to spinat various speeds depending on processing stage, such as a first speedduring a developing process and a second speed during a rinsing process.In some implementations, motion mechanism 354 includes an elevationsystem configured to move wafer stage 352 along a vertical directionand/or horizontal direction, such that workpiece 200 can be positionedat different levels within developing and rinsing system 300. A nozzle356 delivers a developer (e.g., NTD developer 210) to workpiece 200. Insome implementations, nozzle 356 dispenses NTD developer 210 whileworkpiece 200 is spun by wafer stage 352. NTD developer 210 can bestored in a container 358 and then be delivered to nozzle 356 via adelivery system (e.g., a pump, a pressurized gas, or other mechanismconfigured to deliver the developer via one or more pipelines to nozzle356). As described above, NTD developer 210 includes one or more organicsolvents. In some embodiments, organic solvents are pre-mixed and storedin container 358. Alternatively, organic solvents are stored in separatecontainers and mixed through the delivery system as NTD developer 210 isapplied to workpiece 200. After NTD developer 210 is spun off workpiece200, drain outlet 370 guides NTD developer 210 out of developing andrinsing system 300, for example, towards a waste process system.

In some implementations, developing and rinsing system 300 applies NTDdeveloper 210 in a spin-on process, for example, by spraying NTDdeveloper 210 onto resist layer 206 while spinning workpiece 200. Insome implementations, NTD developer 210 is continuously sprayed ontoworkpiece 200. Alternatively, in some implementations, NTD developer 210is applied by other means, such as a puddle process. In someimplementations, developing and rinsing system 300 is part of a clustertool in an IC fabrication process. For example, after resist layer 206has been exposed in a lithography system, workpiece 200 is transferredto developing and rinsing system 300.

Following the development process, another nozzle 366 delivers a rinsesolution (e.g., rinse solution 216) to workpiece 200. In someimplementations, nozzle 366 dispenses rinse solution 216 onto patternedresist layer 206′ in ways similar to the dispensing of NTD developer210. Rinse solution 216 can be stored in a container 368 and then bedelivered to nozzle 366 via a delivery system (e.g., a pump, apressurized gas, or other mechanism configured to deliver the developervia one or more pipelines to nozzle 366). As described above, rinsesolution 216 includes water and one or more organic solvents. In someembodiments, components of rinse solution 216 are pre-mixed and storedin container 368. In some implementations, developing and rinsing system300 controls a mixing ratio between various components of rinse solution216.

After rinse solution 216 is spun off workpiece 200, drain outlet 370guides rinse solution 216 out of developing and rinsing system 300, forexample, towards a waste process system. Note that both NTD developer210 (organic solution with no water) and rinse solution 216 (with water)may be guided out of system 300 by the same drain outlet 370. In otherwords, the organic solution and water-based solution may be delivered tothe same waste process system. This is different from existingdeveloping and rinsing systems where organic solutions and water-basedsolutions are delivered to and processed by separate waste processsystems.

Note that developing and rinsing system 300 can include additionalfeatures depending on implemented lithography process technologies. FIG.4 has been simplified for the sake of clarity. Additional features canbe added in developing and rinsing system 300, and some of the featuresdescribed below can be replaced or eliminated for additional embodimentsof developing and rinsing system 300.

The present disclosure provides various resist rinse solutions andcorresponding lithography techniques for improving structural integrityof patterned resist layers. An example lithography method includesforming a resist layer over a workpiece, exposing the resist layer toradiation, developing the exposed resist layer using a developer thatremoves an unexposed portion of the exposed resist layer, therebyforming a patterned resist layer, and rinsing the patterned resist layerusing a rinse solution. The developer is an organic solution, and therinse solution includes water. In an embodiment, during the rinsing thewater penetrates into the patterned resist layer such that hydrogenbonds are formed between molecules of the water and polar functionalgroups of the patterned resist layer. In an embodiment, the waterconstitutes between about 5% and about 30% of the rinse solution. In anembodiment, the rinse solution further includes a dipolar solvent thatconstitutes between about 5% and about 70% of the rinse solution. In anembodiment, the rinse solution includes a solvent that has a surfacetension lower than about 35 dyn/cm. In an embodiment, the solvent thathas a surface tension lower than about 35 dyn/cm constitutes betweenabout 10% and about 70% of the rinse solution. In an embodiment, therinse solution has an overall surface tension greater than about 35dyn/cm. In an embodiment, the rinse solution includes a crosslinkingagent. In an embodiment, the crosslinking agent constitutes betweenabout 0.01% and about 15% of the rinse solution. In an embodiment, theorganic solution of the developer includes n-butyl acetate but includesno water, wherein the rinse solution includes between 5%-30% of water,between 10%-20% of a dipolar solvent, and between 0.01%-15% of acrosslinking agent.

In another example aspect, the present disclosure provides a method forIC manufacturing. The method comprises forming a resist layer over aworkpiece, exposing the resist layer to patterned radiation, removing anunexposed portion of the resist layer in a negative tone developer,thereby forming a patterned resist layer, wherein the negative tonedeveloper includes an organic solvent, and rinsing the patterned resistlayer in a rinse solution, wherein the rinse solution has an overallsurface tension that is higher than a surface tension of the organicsolvent. In an embodiment, the overall surface tension of the rinsesolution is at least about 35 dyn/cm against air, and wherein thesurface tension of the organic solvent is less than about 35 dyn/cmagainst air. In an embodiment, the rinse solution has an overallpolarity that is higher than both a polarity of the patterned resistlayer and a polarity of the organic solvent. In an embodiment, the rinsesolution includes between about 5% and about 30% of water and betweenabout 5% and about 70% of a dipolar solvent. In an embodiment, the rinsesolution further includes between 0.01%-15% of a crosslinking agent. Inan embodiment, the rinse solution further includes a solvent that has asurface tension lower than about 35 dyn/cm. In an embodiment, the methodfurther comprises after exposing the resist layer and before removingthe unexposed portion of the resist layer, performing a baking processon the resist layer; and after rinsing the patterned resist layer in therinse solution, processing the workpiece using the patterned resistlayer as a mask.

In yet another example aspect, the present disclosure provides a rinsesolution for rinsing a patterned resist layer after NTD. The rinsesolution comprises water, a dipolar solvent, and a crosslinking agent.In an embodiment, the water constitutes between 5% and 30% of the rinsesolution, the dipolar solvent constitutes between 5% and 70% of therinse solution, and the crosslinking agent constitutes between 0.01% and15% of the rinse solution. In an embodiment, the rinse solution furtherincludes a solvent that has a surface tension lower than 35 dyn/cm.

The foregoing outlines features of several embodiments so that those ofordinary skill in the art may better understand the aspects of thepresent disclosure. Those of ordinary skill in the art should appreciatethat they may readily use the present disclosure as a basis fordesigning or modifying other processes and structures for carrying outthe same purposes and/or achieving the same advantages of theembodiments introduced herein. Those of ordinary skill in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the present disclosure, and that they may makevarious changes, substitutions, and alterations herein without departingfrom the spirit and scope of the present disclosure.

What is claimed is:
 1. A method comprising: forming a photosensitivelayer; exposing the photosensitive layer to radiation; developing theexposed photosensitive layer using a developer that removes an unexposedportion of the exposed photosensitive layer, thereby forming a patternedphotosensitive layer; rinsing the patterned resist layer with a rinsesolution, wherein a portion of the developer is disposed on a surface ofthe patterned photosensitive layer during the rinsing of the patternedphotosensitive layer with the rinse solution; and wherein the rinsesolution includes about 1% to about 30% water such that the rinsesolution penetrates through the portion of the developer to modify thepatterned photosensitive layer during the rinsing of the patternedphotosensitive layer.
 2. The method of claim 1, wherein during therinsing the water penetrates into the patterned photosensitive layersuch that hydrogen bonds are formed between molecules of the water andpolar functional groups of the patterned photosensitive layer.
 3. Themethod of claim 1, wherein the developing of the exposed photosensitivelayer using the developer includes applying the developer using a firstapplication process at a first speed; and wherein the rinsing of thepatterned resist layer with the rinse solution includes applying therinsing solution using a second application process at a second speedthat is different than the first speed.
 4. The method of claim 1,wherein the rinse solution further includes a solvent that constitutesbetween at least 5% of the rinse solution.
 5. The method of claim 1,wherein the rinse solution includes a solvent that has a surface tensionlower than about 35 dyn/cm.
 6. The method of claim 5, wherein thesolvent that has a surface tension lower than about 35 dyn/cmconstitutes between about 10% and about 70% of the rinse solution. 7.The method of claim 5, wherein the rinse solution has an overall surfacetension greater than about 35 dyn/cm.
 8. The method of claim 1, whereinthe rinse solution includes a crosslinking agent that constitutes about15% or less of the rinse solution.
 9. A method comprising: exposing aphotosensitive layer to radiation; after exposing the photosensitivelayer to radiation, removing a portion of the photosensitive layer in anegative tone developer, thereby forming a patterned photosensitivelayer, wherein the negative tone developer includes an organic solvent;and rinsing the patterned photosensitive layer in a rinse solution,wherein a layer of the negative tone developer is disposed on a surfaceof the patterned photosensitive layer during the rinsing of thepatterned photosensitive layer, wherein the rinse solution includesabout 1% to about 30% water such that the rinse solution penetratesthrough the layer of the negative tone developer to modify the patternedphotosensitive layer during the rinsing of the patterned photosensitivelayer.
 10. The method of claim 9, wherein a surface tension of the rinsesolution is greater than a surface tension of the organic solvent. 11.The method of claim 9, wherein the rinse solution has a polarity that ishigher than a polarity of the patterned photosensitive layer.
 12. Themethod of claim 9, wherein the rinse solution has a polarity that ishigher than a polarity of the organic solvent.
 13. The method of claim9, wherein the rinse solution further includes between about 5% andabout 70% of a dipolar solvent.
 14. The method of claim 9, furthercomprising performing a baking process on the photosensitive layerbefore removing the unexposed portion of the photosensitive layer. 15.The method of claim 9, further comprising using the patternedphotosensitive layer as a mask after rinsing the patternedphotosensitive layer in the rinse solution.
 16. A method comprising:forming a photosensitive layer over a substrate; exposing a firstportion of the photosensitive layer to radiation while a second portionof the photosensitive layer is covered by a material layer; applying anegative tone developer to the photosensitive layer to remove the secondportion of the photosensitive layer to thereby form a patterned resistlayer; and rinsing the patterned photosensitive layer with a rinsesolution, wherein a portion of the negative tone developer remainsdisposed on a portion of the patterned resist layer during the rinsingof the patterned resist layer using the rinse solution, wherein therinse solution includes about 1% to about 30% water such that the rinsesolution has a higher polarity than a polarity associated with at leastones of the patterned photosensitive layer and the negative tonedeveloper.
 17. The method of claim 16, wherein the rinse solution has ahigher polarity than both a polarity of the patterned photosensitivelayer and a polarity of the negative tone developer.
 18. The method ofclaim 16, wherein the rinse solution further includes a dipolar solventand a crosslinking agent.
 19. The method of claim 16, wherein theapplying of the negative tone developer to the photosensitive layer toremove the second portion of the photosensitive layer to thereby formthe patterned resist layer includes applying the negative tone developerusing a first spin process at a first speed; and wherein the rinsing ofthe patterned photosensitive layer with the rinse solution includesapplying the rinsing solution using a second process at a second speedthat is different than the first speed.
 20. The method of claim 15,wherein the rinse solution further includes a dipolar solvent and a lowsurface tension solvent, wherein the dipolar solvent constitutes about10% to about 20% of the rinsing solution, and wherein the low surfacetension solvent constitutes about 60% to about 70% of the rinsingsolution.